Xerographic fusing apparatus



Dec. 2, 1969 J. v. CELY ETAL XEROGRAPHIC FUSING APPARATUS 4 Sheets-Sheet 1 Filed Jan. 15, 1968 INVENTORS.

JAMES V. CELY ROBERT T. RITCHIE BY P ATTORNEY.

Dec. 2, 1969 J. v. CELY ETAL XEROGRAPHIC FUSING APPARATUS 4 Sheets-Sheet 2 Filed Jan. 15, 1968 Dec. 2, 1969 Filed Jan. 15, 1968 4 Sheets-Sheet 3 FIG 4 POWER SOURCE SINGLE REVOLUTION CLUTCH United States Patent 3,481,589 XEROGRAPHIC FUSING APPARATUS James V. Cely and Robert T. Ritchie, Lexington, Ky.,

assignors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Jan. 15, 1968, Ser. No. 697,734 Int. Cl. F27b 9/06; F27d 11/00 US. Cl. 263-6 21 Claims ABSTRACT OF THE DISCLOSURE Appratus for fusing fixable marking material to a supporting surface, such as a copy sheet, in a xerographic or similar copying machine is disclosed. The fusing apparatus comprises a heating unit which is mounted in heat exchange relation with and for movement along the path of travel of the moving copy sheetuThe heating unit moves in the same direction as the moving copy sheet during a fusing operation to substantially lengthen the time that the fusing apparatus is disposed in operative relation with the moving copy sheet. After the marking material forming the image on the copy sheet has been fixed and the copy sheet has been transported from the fusing apparatus, the heating unit is returned to its original starting position. The heating unit and a vacuum plenum are positioned on opposite sides of the path of travel of the moving copy sheet and are easily separated to permit servicing of the various components. The heating unit is moved along the path of travel of the copy sheet by a cam controlled drive mechanism.

The present invention relates generally to the heating and copying arts. More particularly, the invention is concerned with the provision of apparatus for fusing fixable Q marking material to a supporting surface in a xerographic or similar copying machine.

The xerographic copying process is Well known in the art and employs a photosensitive element comprising a layer of photoconductive material supported on a conductive backing substrate. The process normally includes the steps of depositing a uniform electrical charge on the surface of the photosensitive element while maintaining the element in the dark, exposing the charged element to a light image of the original being copied, and then developing the latent electrostatic image with fixable marking material or toner. If the photosensitive element is to be reused, the toner image is transferred to a sheet of plain paper defining a copy sheet, usually with the assistance of an external electrical field and/or pressure. The fusing apparatus fixes the toner image on the copy sheet. The finished copy is then transported to an output hopper where it is acessible to the operator.

Xerographic copying machines have been widely employed to produce high quality copies of random originals in a highly convenient and generally economic manner. A problem encountered in the design and utiliation of xerographic copying machines is the relatively large amount of energy and the extended length of time required to fuse the fixable marking material or toner to the copy sheet. A heat fusing operation is relatively inefiicient from a heat transfer standpoint and the heating unit must have sufiicient capacity to raise the temperature of the toner above its melting point as the copy sheet is moved through the fusing apparatus. This problem has recently become much more critical as attempts are made to provide faster xerographic copying machines which produce more copies in a given period of time. Higher speed operation of the copying machine necessarily implies that the copy sheets will be traveling at higher rates of speed and the fusing operations must take place in shorter time intervals.

The above problem has led to the requirements of 3,481,589 Patented Dec. 2, 1969 special electrical wiring sufficient to carry the high amperage electrical currents encountered and large open areas surrounding the copying machine to permit dissipation of the large amounts of heat generated during the fusing operations. These requirements have tended to limit the utilization of copying apparatus to centralized locations where the additional cost of special wiring and necessary space can be justified. Many of the prior art xerographic copying machines require that the heating units or the entire fusing area be at such a high temperature prior to the introduction of a copy sheet that it is necessary to operate the heating units at a low or partially energied level during standby conditions. Also, and most importantly, a prolonged warmup period is often necessary before a copy can be produced when the xerographic copying machine is turned on and prior to the making of the first copy. The long warmup period encountered when the machine is turned on and when making the first or initial copy of an original is a serious inconvenience requiring additional time on the part of the operator.

A xerographic copying machine which is capable of producing copies at relatively high speeds but which does not require special wiring, a large cooling area and an initial prolonged warmup period prior to making the first co-py would have obvious advantages over prior art copying machines. Such a machine could be employed on a de-centralized oflice type basis. The copying machine could be moved to different ofiice locations as required to meet the demand for copies since it could be plugged into any standard volt-l5 ampere outlet.

It is the primary or ultimate object of the invention to provide highly improved fusing apparatus for xerographic or similar copying machines. The fusing apparatus operates to heat the fixable marking material or toner to a temperature above its melting point whereby it adheres to the copy sheet or other supporting surface.

Yet another object of the invention is to provide fusing apparatus which permits the design and construction of a xerographic copying machine capable of producing copies at relatively high speeds but which does not require special wiring or extensive cooling space. The xerographic copying machine can be connected to standard electrical circuits.

Another object of this invention is the provision of fusing apparatus that allows the design and construction of a xerographic copying machine capable of producing copies at relatively high overall speeds without a warmup time prior to the production of the first copy. The accomplishment of this object is considered extremely significant since a minimum of time is required to produce the first copy under all operating conditions, even when the machine is operated after having been idle for an extended period of time. This greatly increases the overall utility of the xerographic copying machine since the average operator time required to produce the average number of copies of an original is substantially reduced.

A further object of the invention is to provide more efficient fusing apparatus for a xerographic copying machine which substantially increases the length of time during which the copy sheet is in operative relation in the fusing apparatus. This object is accomplished by mounting the heating unit for movement along the path of travel of the copy sheets. The heating unit moves along the path of travel in the same direction as and at a slower speed than the copy sheet during a fusing operation. The result of this arrangement is that the relative movement between the heating unit and the copy sheet is reduced.

Yet a further object of the invention is the provision of fusing apparatus for a xerographic copying machine having highly reliable and simplified means for mounting the heating unit for movement along the path of travel of the copy sheets. This mechanism comprises a cam controlled drive mechanism that moves the heating unit along the path of travel of the copy sheets during a fusing operation and then quickly returns the heating unit to its starting position in preparation for the next fusing operation.

Yet a further object of the invention is to provide fusing apparatus for a xerogra-phic copying machine which permits easy access to the interior of the apparatus for maintenance and clearing of paper jams. The heating unit and a vacuum plenum are mounted on opposite sides of the path of travel of the copy sheet. These elements are easily separated to expose the interior of the fusing apparatus.

A further object of the invention is to provide fusing apparatus for a xerographic copying machine having the characteristics set forth above which is extremely simple in construction and operation. The fusing apparatus is fabricated at a relatively low cost and is highly reliable.

The foregoing and other objects and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic side view of a xer'ographic copying machine employing fusing apparatus having a traversing heating unit constructed and operated in accordance with the teachings of this invention;

FIGURE 2 is a fragmentary side sectional view as seen from the opposite side of the xerographic copying machine in relation to the view of FIGURE 1 showing in more detail the construction of the fusing apparatus;

FIGURE 3 is an enlarged and fragmentary side sectional view of the traversing heating unit showing particularly the quartz heating lamp and the reflector therefor;

FIGURE 4 is a plan view of the fusing apparatus which particularly illustrates the cam controlled drive mechanism for moving the traversing heating unit;

FIGURE 5 is a plan view of the vacuum plenum; and

FIGURE 6 is a fragmentary end sectional view taken generally along the section line 6-6 of FIGURE 2.

XEROGRAPHIC COPYING MACHINE Referring now to the drawings, and initially to FIG- URE 1 thereof, there is shown a schematic representation of a xerographic copying machine embodying the fusing apparatus of the present invention. The electrophotographic member of the copying machine comprises a drum 10 which is mounted for rotation in the direction indicated by arrow 11. Disposed on the outer periphery of the drum is a thin layer of photosensitive material 12 which is supported on a conductive substrate. The photosensitive material is preferably an organic photoconductor comprising a one-to-one molar ratio of polymerized vinylcarbazole and 2,4,7 trinitro 9-fiuorenone which is disclosed and claimed in an application of Meredith D. Shattuck and U10 Vahtra entitled Organic Photoconductive Compositions and Their Use in Electrophotographic Processes, Ser. No. 556,982, filed June 13, 1966 and assigned to the assignee of this invention. The photoconductor is coated on a flexible conductive backing material and stored on reels within the interior of the drum to permit replacement or changing of the operative photoconductor surface Without removing the drum from the machine as is disclosed and claimed in an application of Clifford E. Herrick, Jr., entitled Electrophotographic Process, Ser. No. 649, 162 filed June 27, 1967 and assigned to the assignee of the present invention. While the disclosed photoconductor and drum construction are preferred, the present invention is concerned with fusing apparatus and is not dependent on the use of any particular electrophotographic member.

Disposed about the periphery of the drum 10 are a number of processing stations which carry out the cOnventional steps of the xerographic copying process. An initial charging station is provided by a corona unit 13 which deposits a uniform charge on the surface of the photosensitive material while the same is maintained in the dark. The next station is exposure station 14 where a line image of the original document is projected onto the uniformly charged surface of the photosensitive material 12 as the drum rotates. A document 15 to be copied is supported face down on a movable and transparent copy bed 16 which moves back and forth past a scanning slit as indicated by the arrow 17. The document 15 passing the scanning slit is illuminated by lights 18 and a line image of light and shadow is projected by stationary lens 19 onto the photosensitive material 12 carried by the drum.

The next station in the direction of rotation of the drum 10 is a cascade developer unit 20 where a two component developer composition is caused to move across the surface of the drum. The developer composition comprises heat fixable marking particles or toner which is attracted to and deposited on the surface of the photosensitve member in accordance with the latent electrostatic image corresponding to the original. The result of the cascade development operation is the formation of a toner image on the surface of the drum. It is now necessary to transfer the toner image to a copy sheet and this is accomplished at the toner transfer station 22.

The plain copy paper is stored within the copying machine in roll form as indicated by roll 24 and is fed along a path of travel 25 in the direction indicated by the arrows leading past knives 26, toner image transfer station 22, fusing apparatus generally indicated by reference numberal 27 and then to an output copy hopper 28. The copy paper is cut to the length selected by the operator and the cut copy sheet moves into contact with the drum. A transfer corona unit 29 assists in the transfer of the toner image to the copy sheet. The copy sheet is then separated from the drum, the toner image fused by heat and the final copy transported to the output hopper 28.

Not all of the toner image is transferred to the copy sheet and it is necessary to remove the residual toner from the surface of the drum. This is accomplished by employing a pre-clean corona unit 30 whose corona discharge tends to loosen the remaining toner particles and a cleaning brush 31 which is rotated at high speed in the direction indicated by arrow 32. The toner particles which are brushed from the surface of the photosensitive material are drawn by vacuum into a filted bag mounted within a housing 33.

The above description of a representative xerographic copying machine is not intended to limit in any manner the teachings or claims of this invention. The principles of the fusing apparatus disclosed in this specification can be employed with any of a Wide variety of copying systems or machines where it is necessary to fuse toner particles to or otherwise heat a moving copy sheet.

FUSING APPARATUS The fusing apparatus 27, as shown in FIGURES l and 2 of the drawings is located along the upwardly inclined path of travel 25 of the copy sheets between the toner image transfer station 22 and the output hopper 28. It comprises an elongated and stationary vacuum plenum 35 located below the path of travel which provides a means for supporting and transporting copy sheets through the fusing apparatus and a heating assembly 36. The heating assembly 36 is positioned above the path of travel 25 of the copy sheets in opposed overlying relation with respect to the vacuum plenum 35. The operative element of the heating assembly 36 is a heating unit 37 provided by a quartz heating lamp 38 and a reflector 39. The lamp 38 and the reflector 39 are elongated and extend transversely across the path of travel of the copy sheets. The inner surface 40 of the reflector 39 is generally elliptical and highly specular. The heating lamp 38 is connected to a source of electrical energy which is preferably a standard and conventional electrical outlet found in any room since special wiring for supplying the necessary electrical power is not required. The heating lamp 38 and the reflector 39 cooperate to produce a transversely extending and relatively narrow band of infrared radiation on the surface of a copy sheet which, because of the unique mounting and movement of these members, is suflicient to fuse the toner image of the copy sheet.

The heating lamp 38 is preferably clip or spring mounted at its ends within the reflector 39 to permit easy removal and replacement. The reflector is formed from good heat conducting material and has a pair of upturned and vertically extending end walls 41 which nestingly receive and are joined to the depending legs of an elongated and transversely extending channel shaped carriage member 42. Wires 43 for supplying electrical power to the heating lamp 38 run the length of the heating unit 37 in the space between the reflector 39 and the carriage member 42.

Connected to each end of the reflector 39 and the carriage member 42 is a mounting bracket 44 which carries a roller 45. The rollers 45 at the opposite ends of the heating unit 37 engage and ride on the outer upper edges of a large and generally U-shaped heating assembly housing member 46. The upper surface of the carriage member 42 is provided with a pair of buttons 47 at each end thereof. The buttons are formed from a material having a low coeflicient of friction and engage the outer lower edges of the housing member in opposed relation to the rollers 45.

The heating assembly housing member 46 generally overlies the vacuum plenum and its outer side edges define a pair of transversely spaced and longitudinally extending side rails 48 which are engaged on the top and bottom by the rollers 45 and the pairs of buttons 47 at opposite ends of the transversely extending heating unit 37. The arrangement is such that the heating unit 37 comprising the heating lamp 38 and the reflector 39 is mounted in a highly simplified but rugged manner for traversing movement back and forth along the path of travel 25 of the copy sheets. In operation, the heating unit 37 moves from an initial position 50 to a final position 50 indicated by the broken line representation of the heating unit as a copy sheet moves along the path of travel 25 through the fusing apparatus. After the fusing operation, the heating unit 37 is returned to its initial position. The cam controlled drive mechanism for moving the heating unit will be described in detail in a following portion of the specification.

The heat required to fuse the toner image to a copy sheet can be expressed in terms of the following generalized time dependent equation:

AQ AT ftzr where:

AQ=heat required to fuse the toner m=mass of the toner C =constant pressure specific heat of the toner AT=temperature rise of the toner required to fuse the same At=time required to fuse the toner to the copy sheet The use of a traversing heating unit 37 permits the effective time (At) during which heating and fusing of the toner occurs to be appreciably extended so that the overall efliciency of the fusing operation is improved. In general, less energy is required using this fusing apparatus than is necessary in prior art apparatus of the same general type where the heating unit is stationary during the fusing operation.

For example, in a constructed embodiment of the invention, the copy sheets move through the fusing apparatus at a speed of four inches per second while the traversing heating unit moves with a copy sheet at a speed of one and two tenths inches per second. The result of moving the heating unit in this manner is that the copy sheet moves two and eight tenth inches per second relative to the heating unit. The approximately thirty percent reduction in the relative speed of travel between the heating unit and the copy sheet compared to similar apparatus employing a stationary heating unit substantially increases the time available to accomplish fusing of the fixable marking material. The heating lamp employed in this constructed embodiment was of the quartz infrared halogen atmosphere type available from Sylvania Electric Products, Inc. and was rated for operation at 1,350 watts, volts. The power requirements were supplied from a conventional 115 volt-15 ampere electrical wall outlet employing standard wiring and the toner images were satisfactorily fused to the copy sheets under all conditions.

A very important aspect of the highly eflicient xerographic fusing apparatus of this invention is that no Warm-up time is required to properly fuse the toner. The fusing apparatus is available for immediate use whereby the first copy is delivered to the output hopper as quickly as the other steps of the xerographic process can be completed and the sheet of copy paper moved through the machine. The time required to produce the first copy is not dependent on the fusing area reaching a predetermined temperature which in turn is dependent on how recently the xerographic copying machine has been used. Further, in the constructed embodiment of the invention, it was not necessary to partially energize the heating lamp during standby conditions. This reduces the overall power requirements for the xe-rographic copying machine and is particularly important in an installation where the machine is used rather infrequently and partial energization of the heating lamp is inefficient.

The drive mechanism for the traversing heating unit 37 is best shown in FIGURE 4 of the drawings since its primary components are mounted on the top surface of the heating assembly housing member 46. A vertically extending shaft 52 is rotatably supported by a collar in the center of the housing member 46. Attached to the shaft 52 are a relatively large cam 54 having profiled camming surface 55 and an upwardly facing bevel gear 56. Meshing with the teeth of the bevel gear 56 are teeth of another and normally related bevel gear 57 which is pinned to the transversely extending drive shaft 58. The bevel gears 56 and 57 provide a right angle drive connection between the drive shaft 58 and the vertical mounting shaft 52. The drive shaft 58 is supported for rotation in the upstanding walls of a pair of brackets 59 attached to opposite sides of the heating assembly houing member 46 and is connected by clutch 60 to a source of mechanical power 61. The clutch 60 is preferably of the single revolution type and is actuated by timing circuits, not shown. The arrangement is such that as the leading edge of a copy enters the fusing apparatus, the clutch 60 is energized and the cam 54 rotates clockwise through a complete revolution. During this time the heating unit 37 moves from its initial position 50 to its final position 50' as the copy sheet moves through the fusing apparatus and then the heating unit returns very quickly to its initial position 50. The activation of the single revolution clutch 60 is, of course, synchronized with the cutting and feeding of the copy sheets, the rotation of the xerographic drum 10 and the movement of the transparent copy bed 16.

A cam follower roll 65 engages the periphery or camming surface 55 of the cam 54 and is located intermediate the ends of one arm 66 of a bellcrank 67. The bellcrank is mounted for pivotal movement about vertically extending pin 68. The cam follower roll 65 is biased into following engagement with the camming surface 55 of the cam 54 by a strong spring 69 which extends from the other and shorter arm of the bellcrank 67 to a stationary anchor pin 70 on the heating assembly housing member 46. Attached to the outer end of the arm 66 of the bellcrank 67 is a link 71 which carries at its ends a pair of pulleys 72 and 73. Entrained about these pulleys are the opposite ends of a non-extensible and fixed length cord 75. As the pulleys 72 and 73 move back and forth in an arc defined by the length of the bellcrank arm 66 and the shape of the camming sulface 55, the cord 75 is pulled back and forth aong a defined path.

Mounted from the brackets 59 attached to opposlte sides of the heating assembly housing member 46 are pulleys 78-81. These pulleys are located at the corners of the heating assembly housing member and, in combination with additional pulleys 82 and 83 on the housing member 46 and the movable pulleys 72 and 73 carried by link 71, define the path of travel for the cord 75. The cord 75 extends from a stationary mounting point 84 for one end thereof, around movable pulley 72, then about stationary pulleys 83, 79, 78, 82, 81 and 80 on the order indicated, and about movable pulley 73 to one end of a relatively strong spring 85. The other end of the spring 85 is anchored at 86 to the heating assembly housing member 46. The spring 85 is provided to take up any slack in the cord 75 and maintain it tight in its path. The path of the cord 75 is such that the portions 87 and 88 thereof extending between the stationary pulleys 8081and 7 8-79 located on opposite sides of the heating assembly housing member will move in the same direction and by the same distance in response to movements of the movable pulleys 72 and 73 under control of the rotating cam 54 and cam follower roll 65. The mounting brackets 44 located at the opposite ends of the transversely extending heating unit 37 are attached to the cord 75 at the points indicated by the marks 89. The drive mechanism moves the heating unit 37 back and forth between its initial and final posi tions 50 and 50' over the path of travel 25 of the copy sheets in accordance with the profile of camming surface 55 of cam 54 to substantially lengthen the time that a copy sheet remains in operative relation with the heating unit.

The vacuum plenum 35 is shown in detail in FIGURES 2, and 6 of the drawings and comprises a generally elongated and flat housing 90 formed from sheet metal or similar material and having a pair of enlarged pockets 91 and 92 at the ends thereof. Rotatably supported within the pocket 92 is a relatively large diametered drive roll 93. The drive roll 93 has a pair of side flanges and a plurality of transversely spaced ridges 94 which define guiding means for a plurality of transversely spaced endless copy sheet carrying belt 95. The belts are preferably fabricated from heat resistant fabric material having a high coeflicient of friction and may be rubber coated or impregnated to better engage and hold the copy sheets. A power source 96 (see FIGURE 5) is drivingly connected to and continuously rotates the drive roll 93 when the vacuum plenum is latched in its operative position.

Disposed wihtin the housing pocket 91 are a plurality of transversely aligned and belt tensioning rolls 97. One of these rolls is associated with each of the endless copy sheet carrying belts 95. Each of the tensioning rolls 97 is rotatably supported in its individual slidable carrier 98 that is biased by a spring 99 toward the entrance end of the fusing apparatus. Rollers 100 and 101 are journalled in the housing 90 adjacent its ends and further guide the belts 95 along the lower portions of their paths of travel. The arrangement is such that the endless belts 95 are properly guided, tensioned and driven to transport copy sheets through the fusing apparatus.

Supported within and adjacent the top surface of the housing 90 of the vacuum plenum and between the drive roll 93 and the tensioning rolls 97 are a plurality of longitudinally extending sheet metal plates or slats 103. The plates 103 provide the top surface of the vacuum plenum and support the endless belts along the upper portions of their paths of travel. These plates are transversely spaced from each other to define longitudinally extending openings or slits 104 between the transversely spaced endless copy sheet carrying belts 95. In addition, a pair of slots 105 are formed in the outermost pair of plates 103 and underlie the two rows of apertures 106 provided in the outermost of the endless belts 95 The slits 104 between the plates, the spaces between the adjacent edges of the endless belts, the slots 105 and the rows of apertures 106 define a plurality of longitudinally extending and transversely spaced ports for applying vacuum pressure to the back of a copy sheet as it is transported through the fusing apparatus. The copy sheet is firmly held to the driven endless belts without disturbing the toner image on the face of the copy sheet or interfering in any way with the fusing operation. It is noted that the transverse spacing between the two rows of apertures 106 in the outermost belts is approximately equal to the width of the copy sheets. This has been found particularly effective in preventing curling of the side edges of the copy sheet due to thermal shock caused by the very rapid evaporation of moisture from the copy sheet.

One side of the vacuum plenum housing 90 is formed with an elongated and vertically tapered vacuum port 108 that is best shown in FIGURE 6 of the drawings. The port 108 cooperates with the complementary tapered end of a passageway 109 which extends from the stationary frame of the xerographic copying machine. The passageway 109 is in communication with a vacuum source 110. The various adjacent edges of the vacuum port 108 and passageway 109 are overlapped to reduce the loss of vacuum pressure. This arrangement, while being sufficiently fluid tight to prevent undue losses in vacuum pressure, permits the vacuum plenum to be pivoted down to an open position without requiring disconnection of vacuum lines or any other special operations on the part of the operator. Also, the use of flexible vacuum lines or conduits which require relative frequent replacement has been avoided.

The end of the vacuum plenum 35 at the entrance to the fusing apparatus is pivoted to the stationary frame of the xerographic copying machine by a pair of laterally projecting pivot pins 116. The other end of the vacuum plenum 35 carries a pair of transversely extending locking pins 117 which cooperate with a pair of spring biased latches 118 that are pivotally mounted from the frame of the xerographic copying machine. This mounting arrangement for the vacuum plenum is highly advantageous since the operator need only release the latches 118 and the vacuum plenum is pivoted down to about pivot pins 116 to completely expose the interior of the fusing apparatus. Any jams of copy sheets within the fuser apparatus can be quickly cleared and routine maintenance, such as periodic replacement of the quartz heating lamp 38, is greatly facilitated. The latches 118 are of the self latching type and are designed to automatically engage and latch the locking pins 117 in the position shown in FIGURE 2 of the drawings when the vacuum plenum is pivoted upwardly to its closed position.

The vacuum has been found quite effective in conveying copy sheets through the fusing apparatus without jamming. However, jams of copy sheets may occur on a very infrequent basis and a fire hazard can exist under these conditions if the copy sheets contact or comes too close to the heating lamp or other portions of the heating unit. To eliminate this hazard, it is possible to insert a wire grille, not shown, between the path of travel of the copy sheets and the heating unit. The grille prevents a copy sheet from getting close enough to the heating unit to become overheated and start a fire under fault conditions. Alternately, the apparatus disclosed and claimed in the copending patent application of Glenn F. Siemer, Ser. No. 722,285, filed Apr. 18, 1968, entitled Safety Arrangement for Xerographic Copying Apparatus and which is also assigned to the assignee of the present invention can be employed. As disclosed in this copending application, the drive mechanism is effectively disconnected from control of the drive cam and the heating unit is quickly moved to a shielded safety position out of operative heating relation with the copy sheet OPERATION Considering now the operation of the xerographic fusing apparatus of this invention, it will be assumed that the heating unit 37 is in its initial position 50 and the endless belts 95 are being driven in a direction to advance copy sheets upwardly through the fusing apparatus along the path of travel 25. As a copy sheet having a toner image thereon is stripped from the drum, it is transported into the fuser apparatus over a guide 119 located at the entrance end of the vacuum plenum (see FIGURE 2). When the leading edge of the copy sheet enters the fusing apparatus, the synchronizing timing circuits actuate the single revolution clutch 60 so that cam 54 is rotated clockwise through a complete revolution. The rise of the cam surface 55 is such that the heating unit 37 advances in the same direction as the copy sheet at a substantially constant velocity. As previously explained, the velocity of the heating unit 37 is less than that of the copy sheet, but it is sufficient to substantially increase the time that the heating unit is in operative fusing relation with the copy sheet. During its movement through the fusing apparatus, the copy sheet is held in a flat condition by the vacuum pressure applied to the back of the sheet.

As the trailing edge of the'copy sheet with the fused image thereon leaves the fusing apparatus, the heating unit 37 has reached its final position 50'. The cam follower roll 65 moves from the highest rise portion to the dwell of the cam 54 and the heating unit returns quickly to its initial position under the action of spring 69. The length of time required to return the heating unit to its initial position is very short so that it is ready to fuse the toner image to the next copy sheet When the latter is introduced into the fusing apparatus.

It should now be apparant that the objects initially set forth have been accomplished and that various changes can be made in the disclosed embodiment without departing from the teachings of the invention. For example, the shape of the drive cam can be selected in accordance with the heating the heating unit which is desired or required for any particular application. The heating unit may comprise more than one heating lamp or other types of heating elements. Also, the fusing apparatus has applications, in a wide variety of copying systems other than those employing dry toner particles. t1 may be used to evaporate the solvent from and/ or dry copy sheets in a copying system employing liquid development techniques and the term fusing as employed in this specification and the claims is intended to include and cover the use of disclosed method and apparatus for these purposes.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the :art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Apparatus for heating a moving copy sheet in a copying system or the like comprising:

means to move a copy sheet in one direction along a path of travel;

a heating unit located in heat exchange relation with a copy sheet moving along said path of travel; means mounting said heating unit for movement in said one direction along said path of travel; and

means to move said heating unit along said path of travel in said one direction when a copy sheet is moving along said path of travel in said one direction adjacent said heating unit to extend the time the copy sheet is in heat exchange relation with said heating unit. 2. Apparatus for fusing an image on a copy sheet in a copying system comprising:

means to move a copy sheet in one direction along a path of travel; a fusing unit located in fusing relation with a copy sheet moving along said path of travel; means mounting said fusing unit for movement in said one direction along said path of travel; and means to move said fusing unit along said path of travel in said one direction when a copy sheet is moving along said path of travel in said one direction adjacent said fusing unit to extend the time the copy sheet is in fusing relation with said fusing unit. 3. Apparatus according to claim 2 further characterized by:

said fusing unit comprises a heating unit disposed in heat exchange relation with a copy sheet moving along said path of travel. 4. Apparatus for fusing an image on a copy sheet in a copying system or the like comprising:

.means to move a copy sheet in one direction along a path of travel; a fusing unit located in fusing relation with a copy sheet moving along said path of travel; means mounting said fusing unit for movement along said path of travel in said one direction from an initial position to a final position; and means to move said fusing unit from said initial position to said final position when a copy sheet is moving along said path of travel adjacent said fusing unit to extend the time the copy sheet is in fusing relation with said fusing unit. b 5. Apparatus according to claim 4 further characterized said fusing unit comprises a heating unit disposed in heat exchange relation with a copy sheet moving along said path of travel. 6. Apparatus according to claim 4 further characterized by:

said means to move said fusing unit comprises means to return said fusing unit from said final position to said initial position after a copy sheet has moved from fusing relation with said fusing unit. b 7. Apparatus according to claim 6 further characterized said means mounting said fusing unit comprises a pair of spaced rail means; and a fusing unit suporting carriage having a pair of spaced guiding means engaging said pair of spaced rail means.

b 8. Apparatus according to claim 7 further characterized said means to move said fusing unit comprises a rotatable cam; and cam follower means interconnecting said rotatable cam and said fusing unit supporting carriage. 9. Apparatus for fusing an image on a copy sheet in a copying system or the like comprising:

means to move a copy sheet in one direction along a path of travel; a fusing unit located in fusing relation with a copy sheet moving along said path of travel; means mounting said fusing unit for movement along said path of travel in said one direction from an initial position to a final position and for return of said fusing unit from said final position to said initial position; means to move said fusing unit from said initial position to said final position when a copy sheet is moving along said path of travel adjacent said fusing unit to extend the time the copy sheet is in fusing relation with said fusing unit;

said means to move said fusing unit comprising a cam;

cam follower means interconnecting said cam and said fusing unit; and

means to effect relative movement between said cam and said cam follower means.

10. Apparatus according to claim 9 further characterized by:

said cam follower means comprises a cam follower element engaging said cam;

a plurality of relatively stationarily mounted rotatable pulleys and at least one rotatable pulley which is mounted for translational movement;

a linkage means rigidly interconnecting said cam follower element and said pulley which is mounted for translational movement;

a flexible member extending in a path of travel about said pulleys; and

said fusin unit being connected to said flexible mem ber so that said fusing unit moves along said path of copy sheet travel upon actuation of said means to effect relative movement between said cam and said cam follower means.

11. Apparatus according to claim 10 further characterized by:

an elongated housing member positioned to one side of said path of copy sheet travel;

said fusing unit and said cam follower means being positioned on opposite sides of said elongated housing member; and

i a vacuum plenum positioned on the other side of said path of copy sheet travel.

12. Apparatus according to claim 11 further characterized by:

means mounting said vacuum plenum and said elongated housing unit for relative movement generally transverse to said path of copy sheet travel to expose the interior of the fusing apparatus.

13. Apparatus for fusing an image on a copy sheet in a copying system or the like comprising:

means to move a copy sheet in one direction along a path of travel;

said means to move a copy sheet comprising a copy sheet transporting assembly located on one side of said path of copy sheet travel;

a fusing unit located in fusing relation with and on the other side of said path of copy sheet travel in overlying relation with respect to said paper transporting assembly;

means mounting said fusing unit for movement along said path of travel in said one direction from an initial position to a final position; and

means to move said fusing unit from said initial position to said final position when a copy sheet is moving along said path of travel adjacent said fusing unit to extend the time the copy sheet is in fusing relation with said fusing unit.

14. Apparatus according to claim 13 further characterized by:

a stationary machine frame;

means pivoting one end of said copy sheet transporting assembly to said frame;

latch means extending from said frame for releasably holding the other end of said transport assembly in operative position adjacent said path of copy sheet travel and said fusing unit; and

said copy sheet transporting assembly being pivoted away from said path of copy sheet travel to expose the interior of the fusing apparatus when said latch means is released.

15. Apparatus according to claim 13 further characterized by:

means mounting said copy sheet transporting assembly and said fusing unit for relative movement generally transverse to said path of copy sheet travel to expose the interior of the fusing apparatus.

16. Apparatus according to claim 15 further characterized by:

said copy sheet transporting assembly comprises a pair of transversely extending guiding means spaced apart along said path of copy sheet travel;

at least one endless belt extending about said pair of guiding means;

means to drive said belt to advance a copy sheet in said one direction; and

means to apply vacuum pressure to a copy sheet within the fusing apparatus to hold the coply sheet to said belt. 17. The method of fusing marking material to a copy sheet which comprises the steps of:

moving the copy sheet bearing the marking material in one direction along a path of travel; and

moving a fusing unit loacted adjacent said path of travel in said one direction when the copy sheet is moving along said path of travel in said one direction adjacent said fusing unit to extend the time the copy sheet is in fusing relation with said fusing unit. 18. The method according to claim 17 further comprising the steps of:

moving said fusing unit in said one direction from an initial position to a final position at a speed of travel less than the speed of travel of the copy sheet; and

returning the fusing unit from said final position to said initial position when the coply sheet moves from fusing relation with said fusing unit.

19. Apparatus for heating a moving copy sheet in a copying system having a moving image carrying element traveling at a first speed and a transfer station for transferring an image from said moving image carrying member to said copy sheet cmoprising:

means to move said copy sheet to said transfer station and into adjacent facing relation with said movable image carrying member to cause transfer of an image to said copy sheet as said moving image carrying member and said copy sheet both move at said first speed in adjacent facing relation with respect to each other;

means to transport a copy sheet with a transferred image thereon from said transfer station in one direction along a path of travel; a heating unit located in heat exchange relation with a copy sheet moving along said path of travel; and

means for causing relative movement between a copy sheet moving along said path of travel and said heating unit as the copy sheet moves along said path of travel adjacent said fusing unit so that the copy sheet travles relative to said heating unit at a second speed which is slower than said first speed to extend the time the copy sheet is in fusing relation with said fusing unit. 20. Apparatus according to claim 19 further characterized by said means for causing relative movement comprising:

means mounting said heating unit for movement in said one direction along said path of travel; and

means to move said heating unit along said path of travel in said one direction when a copy sheet is moving along said path of travel adjacent said heating unit.

21. Apparatus for heating a moving copy sheet in a copying system having a station for providing an image on a copy sheet comprising:

means to move said copy sheet to said station to provide an image on said copy sheet as said moving image carying member moves at a first speed;

means to transport a copy sheet with an image thereon from said station in one direction along a path of References Cited travel; a heating unit located in heat exchange relation with a UNITED STATES PATENTS copy sheet moving along said path of travel; and 2,496,814 2/1950 Powers 263-6 X means for causing relative movement between a copy 5 33191326 11/1965 Huntsheet moving along said path of travel and said 3,340,618 9/ 1967 Bentzman XR heating unit as the copy sheet moves along said path 3,398,259 8/1968 Tfegay et 219-388 X of travel adjacent said fusing unit so that said co sheet moves relaitve to said heating unit at a secor ig JOHN CAMBY Pnmary Exammer speed which is slower than said first speed to extend U S Cl X R the time the copy sheet is in fusing relation with said fusing unit. 2l9388 

